The present invention relates generally to the field of waveguides. In particular, the present invention relates to photodefinable compositions suitable for use in forming optical waveguides. The invention further relates to methods of forming optical waveguides. As well, the invention relates to optical waveguides and to electronic devices that include an optical waveguide.
Light is becoming increasingly important in the transmission of data and communications. For example, fiber optic cables have replaced conventional electrical cables in a number of applications. Optical waveguides typically include a core material and a cladding layer surrounding the core material. Optical radiation propagates in the core material and is contained by the cladding layer, which has a lower index of refraction than the core material. Waveguides may be used individually or as an array supported on a substrate, and typically transmit optical radiation across a substrate surface. The waveguides often perform a passive function on the optical radiation so as to modify the output signal from the input signal in a particular way. For example, splitters divide an optical signal in one waveguide into two or more waveguides; couplers add an optical signal from two or more waveguides into a smaller number of waveguides; and wavelength division multiplexing (“WDM”) structures separate an input optical signal into spectrally discrete output waveguides, usually by employing either phase array designs or gratings. Spectral filters, polarizers, and isolators may be incorporated into the waveguide design. Waveguides may alternatively contain active functionality, wherein the input signal is altered by interaction with a second optical or electrical signal. Exemplary active functionality includes amplification and switching such as with electro-optic, thermo-optic or acousto-optic devices.
Known methods of manufacturing waveguides include, for example, manually placing glass fibers into hollowed out areas on a substrate; filling a mold of a desired structure with a polymeric material that is thermally cured and later removed from the mold; and depositing a bulk waveguide material on a substrate, followed by standard photolithography and etching patterning processes using a photoresist on the bulk waveguide layer. Each of these processes has drawbacks, however, such as requiring multiple steps to define the waveguide, potential sidewall roughness issues, limited resolution, and increased labor costs.
The use of photoimageable materials in forming waveguides has also been proposed. Such materials are beneficial in that waveguides can be formed using fewer processing steps than the above-mentioned conventional processes. In developing the present invention, the use of various hydroxybenzylsilsesquioxanes to create a photoimageable waveguide has been proposed. It was thought that provision of hydroxy groups on the phenyl ring side groups would allow for development of the composition in aqueous hydroxide solutions. From a processing standpoint, the ability to use an aqueous developer solution in place of a solvent- (i.e., organic-) based developer is desirable for various reasons. For example, aqueous developers can be safely disposed of in an environmentally friendly manner and pose no health risk to those persons handling such materials, in contrast to solvent-based developers. It has since been determined, however, that the optical loss characteristics for waveguides formed from the proposed hydroxybenzylsilsesquioxane materials is higher than desired at certain wavelengths. For example, relatively high absorption at 1550 nm wave energy, one of the important wavelengths employed in the optoelectronics industry, has been observed in such materials. The result is optical loss at that wavelength. Such loss is believed to be due to an excessively high content of hydroxy groups in the photoimageable material.
There is thus a need in the art for compositions suitable for use in manufacturing photoimageable optical waveguides having improved optical loss characteristics while also maintaining developability in an aqueous developer solution. As well, there is a need in the art for waveguides formed from these compositions, for methods of forming such waveguides, and for opto-electronic devices which include such waveguides.